Titanium (Ti) films are widely used in conjunction with titanium-nitride (TiN) as adhesion and barrier layers for the metallization of integrated circuits (ICs). These films are desirable because of several favorable characteristics, including electrical conductivity, corrosion resistance, strength under temperature stresses, and stability.
Ti films are particularly important to microelectronics technology in obtaining low contact resistance to the underlying silicon device. Typically, this is achieved by reacting titanium with silicon to form low-resistance titanium silicide. TiN films are used as a barrier layer between the metallization and the underlying silicon.
With the ever-increasing complexity and reduced feature-size of ICs, there is a growing need to reliably deposit Ti and TiN layers at the bottom of deep narrow contact holes or vias. In the prior art, Ti and TiN films have been deposited by physical vapor deposition or sputtering techniques. However, such techniques are inadequate for high density ICs because of non-conformal coverage of the deep holes.
Conformality of Ti and TiN films in deep holes has improved with the use of chemical vapor deposition (CVD). By way of example, Japan patent number 3214734 describes TiN film formation by CVD using titanium tetrabromide and nitrogen gases. The prior art has also described the CVD formation of Ti and TiN layers from tetraiodotitanium (TiI.sub.4), and from titanium tetrachloride (TiCl.sub.4). The prior art has also shown that the formation rate of titanium films increases by utilizing plasma enhanced CVD.
Nevertheless, the formation of Ti and titanium silicide films according to the prior art leads to several problems. First, even with plasma enhancement--using the gases taught in the prior art, specifically, hydrogen, argon and titanium halide--the required plasma reaction temperature is still too high, encouraging unwanted diffusion, and risking damage to existing metallization layers. Secondly, titanium films made from titanium halides typically contain too much residual halogen, increasing the risk of corrosion of the metallization layers, and reducing the IC's reliability. Third, silicide formation subsequent to titanium deposition requires balancing between the consumption of surface silicon and deposited titanium.
Accordingly, titanium and titanium nitride bilayers (Ti/TiN), titanium silicide and titanium nitride bilayers (TiSi.sub.x /TiN), and trilayers of titanium, titanium silicide and titanium nitride (TiSi.sub.x /Ti/TiN) are also problematic when manufactured by the teachings of the prior art.
The prior art has also shown that certain difficulties exist in the manufacture of TiN films by CVD. For example, U.S. Pat. No. 4,977,106, entitled "TiN Chemical Vapor Deposition Using TiCl.sub.4 and SiH.sub.4," describes the desirability of forming TiN film by CVD and with higher deposition rates and lower reactor temperatures.
It is, accordingly, one object of the invention to provide processes of forming titanium and titanium silicide bi- and tri-layer films with titanium nitride which reduce the afore-mentioned difficulties.
Another object of the invention is to provide an improved process for generating TiN films by CVD.
These and other objects of the invention will be apparent from the description which follows.